Optical emission devices (OEDs) such as light emitting diodes (LEDs) and lasers have various product uses for lighting, displays, signaling and communication. These OEDs are typically created to emit light in a single particular frequency. In some examples, electromagnetic energy is emitted by the devices. If the emission is within the visible light frequency, then the OEDs could be said to emit light in a single color. Visible light spectrum begins near 750 nm as red and ends near 400 nm as violet light. Infrared light occurs at wavelengths above red visible light, and ultraviolet occurs at wavelengths less than violet visible light. Infrared emission is useful in applications where visibility to the human visual system is not required, including optical communications.
The ability to fabricate optical emission devices within a CMOS IC process is highly desirable as it is well known that integration is a key aspect in both size reduction and cost reduction of electrical systems and products. By fabricating the optical emission devices along with CMOS devices such as transistors, capacitors, resistors and the like in a single device, control circuitry can be formed along with the optical emission devices, forming a commercially useful integrated circuit. Furthermore an optical emission device that has the ability to dynamically vary the emission frequencies is desired as this would be key enabling technology for even more compact signaling devices or more compact display devices for visible light emissions.
Silicon based semiconductors typically produce electromagnetic energy in the form of infrared emissions due to the low quantum efficiency related to the indirect band gap that exists in silicon. Quantum dots formed in silicon have demonstrated higher quantum efficiency compared to bulk silicon, however even within the silicon quantum dots, intra-band transitions of less than ˜1 eV are more prevalent, resulting in invisible infrared emissions when photons are emitted. Emissions of light in the visible spectrum are typically achieved in prior known solutions with devices formed using III-V compounds, such as gallium nitride (GaN), indium phosphide (InP) or indium arsenide (InAs), which have direct band gaps.
U.S. Patent Application Publication No. 2012/00098590, titled “Quantum Electro-Optical Device using CMOS Transistor with Reverse Polarity Drain Implant,” with inventors Edwards et. al., published Apr. 26, 2012, which is co-owned with the present application and which is hereby incorporated by reference in its entirety herein, describes forming a quantum dot device using a CMOS process.
An electron volt (1 eV) is a common unit used in physics and is understood to be approximately equal to 1.6×10−19 joules and a milli-electron volt (1 meV) is approximately equal to 1.6×10−22 joules.
For photon emissions, the energy E and wavelength λ are related by equation 1
                              E          =                                    ℏc              λ                        ⁢                                                  ⁢            where            ⁢                                                  ⁢            h            ⁢                                                  ⁢            is            ⁢                                                  ⁢            the            ⁢                                                  ⁢            Planck            ⁢                                                  ⁢            constant                          ,                                  ⁢                              c            ⁢                                                  ⁢            is            ⁢                                                  ⁢            the            ⁢                                                  ⁢            speed            ⁢                                                  ⁢            of            ⁢                                                  ⁢                          light              .                                                          ⁢              Reduced                        ⁢                                                  ⁢            as            ⁢                          :                        ⁢                                                  ⁢                          E              ⁡                              (                                  e                  ⁢                                                                          ⁢                  V                                )                                              =                                    1239.84187              ⁢                                                          ⁢              e              ⁢                                                          ⁢              V                                      λ              ⁡                              (                nm                )                                                                        EQUATION        ⁢                                  ⁢        1            
Using Equation 1, it can be determined that photon emissions for visible light require at least 1.65 eV for red light and as much as 3.27 eV of energy for violet light. An energy level below 1.65 eV produces invisible infrared light and an energy level that is greater than 3.27 eV would also produce invisible light into the ultraviolet ranges and beyond.
The Heisenberg uncertainty principle, expressed in Equation 2, relates that as a position variable Δx becomes smaller, then the momentum variable Δp correspondingly becomes larger, as the product is a constant:
                                          Δ            ⁢                                                  ⁢            x            ⁢                                                  ⁢            Δ            ⁢                                                  ⁢            p                    =                      ℏ            2                          ⁢                                  ⁢        Where        ⁢                                  ⁢        x        ⁢                                  ⁢        is        ⁢                                  ⁢        position        ⁢                                  ⁢        and        ⁢                                  ⁢        p        ⁢                                  ⁢        is        ⁢                                  ⁢                  momentum          ⁢                                          (                      or            ⁢                                                  ⁢            energy                    )                ⁢                                  ⁢        and        ⁢                                  ⁢        ℏ        ⁢                                  ⁢        is        ⁢                                  ⁢        the        ⁢                                  ⁢        reduced        ⁢                                  ⁢        Planck        ⁢                                  ⁢                  constant          .                                    EQUATION        ⁢                                  ⁢        2            
Because the position variable Δx in Equation 2 can be constrained (for example, by use of a quantum well), it can be seen that as a result the momentum or energy variable Δp can be increased, making the indirect bandgap of silicon irrelevant as a limitation on the energy. Equation 2 suggests the possibility of a device that enables inter-band energy transitions, that is, transitions from conduction-to-valence band transitions, where the electron energy change can be high enough to produce visible light. Further, it is also desirable to create emission devices that are capable of capture and re-emission of visible and invisible photons in a controlled fashion. An optical emission device is desired that can emit light in frequencies that are both invisible and visible, that can receive photons and store energy, and later again convert the stored energy to light emission in a controlled manner. An optical emission device with these functions has many applications, including applications in optical communications and photodetection. For practical and widespread use, the optical emission device should operate at room temperatures.
A continuing need thus exists for an optical emission device that is capable of controlled energy emission including visible light emission and with room temperature operation, and which is an optical emission device that can be fabricated using existing semiconductor process technologies. Further, a need exists for an optical emission device that is compatible with the fabrication of CMOS transistors to enable the production of a single integrated circuit that can include transistors along with the optical emission device.